1. Field of the Invention
This invention relates generally to systems and methods for performing a power system data redundancy check in an electric power system, and more specifically to systems and methods including at least one intelligent electronic device which compares received and derived power system data as an effective way to detect problems such as device failure, monitoring inaccuracies and security issues.
2. Description of Related Art
Electric utility systems or power systems are designed to generate, transmit and distribute electrical energy to loads. In order to accomplish this, electric power systems generally include a variety of power system elements such as electrical generators, electrical motors, power transformers, power transmission lines, buses and capacitors, to name a few. As a result, power systems also include intelligent electronic devices for monitoring, protecting, controlling, metering and/or automating power system elements and associated transmission lines.
It is desirable to transmit power system data between intelligent electronic devices for performing a redundancy check to address device failure, monitoring inaccuracies and security issues, including tampering of the intelligent electronic devices at each respective location. Redundancy checks also improve reliability and service downtime.
In one aspect of the present invention, one or more intelligent electronic devices may be adapted to transmit power system data to another intelligent electronic device. The other intelligent electronic device is adapted to compare the received power system data to its own derived power system data, thereby performing a redundancy check. In this arrangement, a third device is not necessary in achieving redundancy check functionality.
For example, revenue meters are intelligent electronic devices generally used to monitor or record, among other things, power consumption by an end user. It is desirable to perform a redundant or validation check of a revenue meter in order to monitor and ensure the accuracy thereof. This process is typically referred to as redundant metering.
Although the traditional systems as described below generally involve meters, such systems may further be implemented into any intelligent electronic device having redundancy check capabilities. Similarly, although the examples of the multiple embodiments of the present invention described herein sometime refer to “meters”, it should be understood that the apparatus, system, and method described with respect to the present invention herein is applicable any intelligent electronic device having redundancy check capabilities. In addition to meters, examples of such intelligent electronic devices may include among other things protective relays, recloser controls, I/O processor and controllers, communication processors, Synchrophasors, capacitor bank controllers, or any other intelligent electronic devices having redundancy check capabilities.
Traditional systems for providing redundant metering include having an inspector physically monitor the functionality of a meter by comparing such to another meter. Other traditional systems for providing redundant metering functionality, or if providing a redundancy check, between other types of intelligent electronic devices generally require additional components or devices for providing the redundancy check between or among intelligent electronic devices.
For example, another traditional arrangement for providing redundant metering includes implementing a supervisory control and data acquisition (SCADA) system associated with a plurality of meters. In this arrangement, a host computer provides supervisory control over remote terminal units (RTUs). One or more of the RTUs is associated with a plurality of meters. The meters in this arrangement typically include a meter for general revenue metering applications and another meter for sampling selected power system data. Yet another separate intelligent electronic device is required to provide a redundancy check between the two meters. Communication between the meters may be typically controlled and monitored at the host computer or RTU level, and may be achieved through a communication link typically involving transmitting analog current outputs via DNP, modbus, Ethernet or other such data communications protocol. Although this system may be used to achieve real-time monitoring, this system requires a constant communication link, a number of communications components, multiple connections between the meters, and programming by a person trained in communications or SCADA applications. Moreover, this system generally includes a third intelligent electronic device for providing redundancy check functionality. The third device is often located off-site from the other intelligent electronic devices. This off-site location is often less secured, thereby causing this means for transmitting data to also be less secure.
Accordingly, it is an object of the present invention to provide one or more intelligent electronic devices which may be adapted to transmit power system data to another intelligent electronic device, whereupon the other intelligent electronic device is adapted to receive such data and compare the received data to its own power system data, thereby performing a redundancy check therebetween. In this arrangement, a third device is not necessary in achieving redundancy check functionality.
It is further an object of the invention to provide a secure, noise resistant and tamperproof method for providing a redundancy check between intelligent electronic devices, whereupon only one communication link is required. In U.S. Pat. No. 5,793,750, the contents of which are hereby incorporated by reference, a communication system between two microprocessor-based protective relays for an electric power system is disclosed. Each of the two relays in that system has both transmit and receive modules, for directly transmitting indication status bits indicative of the result of selected protective functions of one relay from that one relay to the other, and vice versa.
The output status indication bits are sometimes used to identify the existence and location of a fault on the power line portion served by the two relays. One or both of the relays might initiate a circuit breaker trip action on the basis of the exchange of such information. The output status indication bits may be the result of processing functions in one of the relays involving the voltages and/or currents on the power line. The output status indication bits may be used for various control, status, indication and protection functions. Examples of protection functions include permissive overreaching transfer trip (POTT) actions, permissive under-reaching transfer trip (PUTT) actions, directional comparison unblocking (DCUB) and direct transfer trip (DTT) actions. Other relay-to-relay operations are possible using particular output status indication bits.
The advantage of the communication system described in the '750 application is that it is fast and secure. Protective relays typically accomplish their monitoring functions several times each power system cycle. The '750 communication system provides the results of these monitoring functions of one relay, to the other relay. The information is transmitted directly over a communication link from an originating relay, which may or may not trip its associated circuit breaker based on its operational results, to another relay. The receiving relay then uses the transmitted information, in the form of digital bits, to perform its own on-going calculations, producing various protection actions such as tripping and closing a circuit breaker when appropriate. The communication between the two relays may be bi-directional, allowing the two relays to exchange information concerning the results of their own calculations both quickly and securely, with a minimum amount of expense.
Therefore, it is yet another object of the invention to provide one or more intelligent electronic devices adapted to transmit and receive indication status bits in the form of successive data stream messages indicative of selected power system quantities of one intelligent electronic device from that one intelligent electronic device to the other, and vice versa in order to perform a redundancy check therebetween.